Is an A record for the domain itself mandatory?

[Me]

Thanks for the quick response, Joseph. The MX records are still in place. I
can telnet to port 25 on their mail server and send email using manual SMTP
commands and the mail server's DNS name perfectly, while on my mail server.

Unfortunately they did not get the A record put back today and their DNS
admin won't be back until Friday so I can't find out anything regarding any
other changes.

We did find an MS article that says Exchange 5.5 caches the last 1,000 DNS
lookups regardless of TTL. Nice, huh? Reminds me of their ISA 2000
firewall/proxy server that cached all DNS lookups for eight hours regardless
of TTL or where Windows 2000 Pro cached all negative responses for fifteen
minutes. <sigh>

Ray

"Joseph S D Yao" <jsdy at center.osis.gov> wrote in message
news:e21cnt$1nie$1 at sf1.isc.org...
> On Mon, Apr 17, 2006 at 06:26:48PM -0400, JJ wrote:
> > I guess this is something I haven't run across before. A company we deal
> > with deleted the A record for their domain ("example.com") but left
> > www.example.com in place. They also had two MX records in place, both
> > priority 20, that were different hosts than the www. record.
> >
> > For whatever reason, our Exchange 5.5 mail server suddenly couldn't send
> > them email any more at about the same time, complaining about "host
> > unreachable". They're going to add the A record back tomorrow, but I was
> > wondering if such an A record was mandatory.
> >
> > Thanks for any enlightenment you can share,
> >
> > Ray
>
>
> The A record is absolutely not mandatory.  It used to be rare.
>
> But if they don't have an A record for their domain that is the same as
> their mail server, they must have an MX record for the domain that
> points to the mail server, in order for mail to account at domain to work.
> (An A record pointing to their Web server's IP address, as seems to be
> more common these days, is absolutely irrelevant to e-mail unless there
> is no MX record, in which case it prevents e-mail from working.)
>
> It's not clear from what you are saying that the MX records were kept in
> place (you use the past tense), but you also don't say they were
> deleted.  If they were not deleted, they should have still worked.
>
> Have you investigated whether both mail servers were in fact still
> accessible from your MS Ex server?  Or whether other DNS changes of
> which you had not been aware were also made, and the MS error messages
> were poor as usual?
>
> -- 
> Joe Yao
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